The invention relates to a method of automatically freeing an axis which, after running over a safe end position, is monitored to ascertain when it is at a standstill, and to a corresponding numerical control.
Modern numerical controls can be made available in conjunction with suitable drive system functions, enabling a machine tool manufacturer to equip a machine, such as a numerically controlled machine tool or a robot, with safety technology for protection of the machine and personnel.
One of the monitoring functions included in this is often the monitoring for xe2x80x9csafe end positionsxe2x80x9d, which monitors a numerically movable axis for its absolute position. In this case, the values for the safe end positions are generally parameterized as pairs of position values in machine data, to be specific one limit value in the negative traversing direction, the second limit value for the positive traversing direction of the axis. If one of these limit values is exceeded, a stop response is initiated, which brings the axis to a standstill. In addition, the overshooting of the safe end position is often indicated to the user by an alarm.
Further traversing of the axis in the same direction would lead to a hazardous situation for man and/or the machine, and must be prevented by the machine control system.
For this purpose, two procedures are known from the prior art. On the one hand, this takes place by dependable monitoring of the standstill of the axis or, on the other hand, it takes place by continuous triggering of the alarm belonging to the safe end position and the associated suppression of further traversing commands.
The user/machine operator then conventionally has two possible ways of bringing the machine from this standstill situation back into the normal operating state.
One known possible way is to switch over to alternatively provided safe end positions, which were previously parameterized in the commissioning phase of the machine in such a way that traversing of the axis is possible again, for example by a second pair of limit switches permitting a greater traversing range of the axis.
Apart from increasing the possible traversing range, this obliges the machine manufacturer to parameterize the second available safe end position in this way. Consequently, however, this second safe end position is no longer available for the parameterizing of another, independent traversing range.
Once the axis has been moved into the actual traversing range, limited by the first pair of safe limit switches, it is then possible to switch over to the original safe end position again.
An alternative known procedure comprises temporarily switching off the monitoring for safe end positions. Consequently, the monitoring is no longer active and the axis can be moved in any direction.
Further, the object of the present invention may be achieved as shown in FIG. 2 by a numerical control for the safe moving of an axis which has the following components:
a monitor (M-1) for monitoring a permissible traversing range of the axis within safe end positions;
a monitor (M-2) for monitoring for overshooting of a standstill range by the axis, which can be activated after running over a safe end position; and
a monitor (M-3) for monitoring for overshooting of a freeing range which can be defined by a first limit value in the traversing direction of the axis which led to the overshooting of the safe end position (with the value of the greater limit in absolute terms of the monitored standstill range of the axis) and by a second limit value in the other traversing direction of the axis (with the value of the corresponding safe end position) where it is possible to move the axis back into the normal traversing range within the safe end positions after deactivation of the monitor for monitoring for overshooting of a standstill range, while monitoring for overshooting of this freeing range.
Once the axis has been moved into the actual traversing range of the axis, the monitoring can then be switched on again.
One problem inherent in these conventional measures is consequently the described laborious way of returning from the standstill situation to the normal operating state, on the one hand by use of further safe end positions to be parameterized, which restricts the flexibility and functional scope of the machine, and on the other hand by the alternative laborious operator control of the machine, which may only be carried out by a restricted group of persons.
The recordal of respective actual position values of the axis for activating the various monitors preferrably occurs by a position sensor system (PS-1) or by a pair of limit switches (S-1 and S-2) for recording when the axis runs over a safe end position for activating the monitor for monitoring a permissible traversing range of the axis. A particularly high degree of safety can be achieved by providing the respective monitors means in a two-channel form using dependable technology .
According to the present invention, this object is achieved by a method of automatically freeing an axis which, after running over a safe end position, is monitored to ascertain when it is at a standstill. This is achieved by the following method steps:
switching off monitoring for overshooting the safe end positions;
defining a freeing range by setting a first limit value, in the traversing direction of the axis which led to the overshooting of the safe end position, to the greater limit in absolute terms of the monitored standstill range of the axis and by setting a second limit value, in the other traversing direction of the axis, to the value of the corresponding safe end position;
activating monitoring for overshooting this freeing range;
deactivating the monitoring for a standstill of the axis;
moving the axis back into the normal traversing range within the safe end positions;
activating the monitoring for overshooting the safe end positions; and
deactivating the monitoring for overshooting the freeing range.
Further advantages and details of the present invention will be apparent from the following drawing and description of a preferred embodiment wherein FIG. 1 is a diagram of the speed profile when a monitored axis moves beyond a safe end position. FIG. 2 schematically illustrates a numerical control of the present invention.
According to an advantageous refinement of the method according to the present invention, traversing commands in the traversing direction of the axis which led to the overshooting of the safe end position are additionally inhibited when the monitoring for overshooting of the freeing range is activated. This allows safety to be further enhanced.
Furthermore, the object of the invention is achieved by a numerical control for the safe moving of an axis which has the following components:
a means for monitoring a permissible traversing range of the axis within safe end positions;
a means for monitoring for overshooting of a standstill range by the axis, which can be activated after running over a safe end position; and
a means for monitoring for overshooting of a freeing range which can be defined by a first limit value, in the traversing direction of the axis which led to the overshooting of the safe end position, with the value of the greater limit in absolute terms of the monitored standstill range of the axis, and by a second limit value, in the other traversing direction of the axis, with the value of the corresponding safe end position, it being possible to move the axis back into the normal traversing range within the safe end positions after deactivation of the means for monitoring for overshooting of a standstill range, while monitoring for overshooting of this freeing range.
It is also advantageous within the framework of such numerical control, for the reasons stated, to provide a means for signaling an overshooting of the permissible traversing range.
For further enhancing the safety of such numerical control according to the invention, a means for generating a status signal is provided. This status signal is allocated the value of the safe end position which was overshot. On the basis of this value of the status signal, traversing commands in the traversing direction of the axis corresponding to the value of the status signal can then be inhibited when there is active monitoring for overshooting of the freeing range.
Recording of respective actual position values of the axis for activating the various monitoring means advantageously takes place either by means of a position sensor system or by a pair of limit switches for recording when the axis runs over a safe end position for activating the means for monitoring a permissible traversing range of the axis.
A particularly high degree of safety can be achieved by providing the respective monitoring means in a two-channel form using dependable technology.
A particularly great benefit over the known prior art is that the concept according to the present invention can be performed automatically by numerical control.
Such numerical control according to the invention can be used particularly advantageously in the case of a numerically controlled machine tool or a robot.